1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission.
2. Description of the Related Art
In a typical prior-art control system for automatic vehicle transmissions, the gear ratio of the automatic transmissions is determined by retrieving a predetermined shift program (map) using the vehicle speed and throttle opening as address data.
Moreover, Japanese Laid-Open Patent Application No. Hei 5 (1993)-71625, for example, teaches a control system for automatic vehicle transmission, in which a parameter indicative of the running resistance, more specifically a parameter indicative of the downgrade or upgrade of vehicle running is determined based on the vehicle and throttle opening to select one from among a plurality of shift programs (shift characteristics) for upgrade, downgrade, etc., and the gear ratio is determined by retrieving the selected program by the vehicle speed and throttle opening such that the gear ratio is appropriate both in upgrade or downgrade vehicle running.
Aside from the above, the range of navigation systems extends to embrace everything from simple orientation aids to guidance systems featuring automatic route determination. The navigation system has a road-map memory stored in a CD ROM or the like, and detects the instantaneous vehicle position by, for example, the GPS (Global Positioning System) satellite position system, and provides directional information on a road map including the detected instantaneous vehicle position.
Since the use of such a navigation information enables the recognition or prediction of the details of the road on which the vehicle is traveling, various attempts have been proposed to utilize the navigation information in the control of automatic vehicle transmissions. For example, Japanese Laid-Open Patent Application No. Hei 9 (1997)-303544 teaches a cooperative control with the use of the conventional shift control and the navigation information.
In this prior-art system, there is a gear ratio determined by the upgrade/downgrade control, which determines whether the vehicle is running upgrade or downgrade based on the vehicle acceleration obtained from the transmission output shaft rotational speed (corresponding to the vehicle speed) and the throttle opening. There is also the gear ratio determined by the cooperative control comprising the navigation system and the conventional shift control system. The gear ratio determined under the upgrade/downgrade control is selected if the gear ratio is less than that determined under the cooperation control, while the gear ratio determined under the cooperative control is selected if the gear ratio is equal to or less than that determined under the upgrade/downgrade control.
In this prior-art system, moreover, when the cooperative control is in progress, the gear ratio determined under this control is always selected. The prior-art system, thus, cooperativizes the conventional shift control and the navigation information, giving the priority to the gear ratio determined under the cooperative control so as to prevent the interference therebetween.
However, since the gear ratio determined under the cooperative control has priority over the gear ratio determined under the upgrade/downgrade control, if the navigation system is temporarily invalid, the gear ratio determined under the cooperative control will accordingly not be free from these errors.
Moreover, Japanese Laid-Open Patent Application Hei 9 (1997)-229173 proposes a control system for an automatic vehicle transmission using the navigation system which stores information including the grade of road. In the system, the running resistance is calculated based on the stored information and the detected vehicle speed, and the engine speed and the torque are calculated such that the calculated engine speed and torque are generated with minimum fuel consumption.
However, when the navigation system is configured to have the entire road grade information, the volume of data becomes huge and the calculation become complicated. In addition, this is disadvantageous in cost.
Furthermore, it is sometimes impossible to determine an instantaneous vehicle position accurately based on the navigation information. When this happens, the control response degrades in response to the instantaneous vehicle positional error. In particular this happens when the vehicle running condition changes from upgrade running to level-road running or downgrade running to level-road running.
Furthermore, when the running resistance is calculated based on the road grade in the navigation information, in other words, when no attention is paid to the change in weight of load, it is difficult to determine the running resistance accurately.
Furthermore, the aforesaid prior art (Japanese Laid-Open Patent Application No. Hei 9 (1997)-229173) proposes calculating a proper vehicle speed while the vehicle is cornering, based on the grade of roads in the navigation information, and determining the necessity of deceleration based on the calculated proper vehicle speed, instantaneous vehicle position and the detected vehicle speed such that shift is effected at a timing matched to the vehicle operator""s intention to decelerate.
However, as mentioned above, when the navigation system is configured to have the entire road grade information, the volume of data becomes huge and the calculation become complicated, rendering disadvantageous in cost.
Nevertheless, it is difficult to conduct the shift control appropriately when the vehicle is cornering, without the road grade information. The fact that the necessity of downshift is not the same for a downgrade corner and an upgrade corner, increases the difficulty in this kind of shift control. In any case, it is desirable to effect control to be matched to the intention of the vehicle operator.
An object of this invention is therefore to overcome the aforesaid drawbacks and to provide a control system for automatic vehicle transmission, which determines a parameter indicative of the downgrade or upgrade of vehicle running and selects one from among a plurality of shift programs (shift characteristics) so as to determine the gear ratio appropriate for upgrade/downgrade running, and which determines the gear ratio more appropriately by incorporating the navigation information in the shift control, while preventing the gear ratio determination from being affected by the navigation information if the navigation information is temporarily invalid.
Another object of this invention is therefore to overcome the aforesaid drawbacks and to provide a control system for automatic vehicle transmission, which determines a parameter indicative of the downgrade or upgrade of vehicle running and selects one from among a plurality of shift programs (shift characteristics) so as to determine the gear ratio appropriate for upgrade/downgrade running, and which determines the gear ratio more appropriately by incorporating navigation information of reduced volume in the shift control, while preventing the gear ratio determination from being affected by the navigation information if the navigation information is temporarily invalid and thus preventing the control response from being degraded.
Yet another object of this invention is therefore to overcome the aforesaid drawbacks and to provide a control system for automatic vehicle transmission, which determines a parameter indicative of the downgrade or upgrade of vehicle running and selects one from among a plurality of shift programs (shift characteristics) so as to determine the gear ratio appropriate for upgrade/downgrade running, and which determines the gear ratio more appropriately by incorporating the navigation information in the shift control, while making it unnecessary for the navigation information to include the grade of roads, while estimating the weight of load to correct the grade parameter by the estimated weight of load.
Yet still another object of this invention is therefore to overcome the aforesaid drawbacks and to provide a control system for automatic vehicle transmission, which determines a parameter indicative of the downgrade or upgrade of vehicle running and selects one from among a plurality of shift programs (shift characteristics) so as to determine the gear ratio appropriate for upgrade/downgrade running, and which determines the gear ratio more appropriately by incorporating the navigation information in the shift control, while making it unnecessary for the navigation information to include the grade of roads, while enabling to conduct the shift control when cornering on a specific road, in particular a downgrade road or a level road so as to match the intention of the vehicle operator, thereby enhancing the drivability.
In order to achieve the objects, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting output torque generated by the engine to the driven wheels through the output shaft, comprising: operating condition detecting means for detecting operating conditions of the engine and the vehicle including at least a vehicle speed and a throttle opening; grade parameter determining means for determining a grade parameter indicative of upgrade or downgrade of a road on which the vehicle runs; shift program selecting means for selecting one from among a plurality of shift programs based on the determined grade parameter to determine a gear ratio based on the selected shift program; road information outputting means for determining an instantaneous vehicle position and for outputting road information including that at the determined instantaneous vehicle position; and grade parameter correcting means for correcting the grade parameter based on at least one of the outputted road information and the grade parameter; wherein the shift program selecting means selects the one from among a plurality of shift programs based on the corrected grade parameters to determine the gear ratio based on the selected shift program.